This invention relates to an earth working tooth with wear cap and, more particularly, to a uniquely contoured and constructed wear cap that promotes longer life of the tooth. The tooth with which the instant invention is concerned includes an adapter which is designed to be fastened so as to project forwardly from the leading edge of earth working equipment, i.e., buckets, dippers, etc. At the projecting forward end of the adapter, a nose is normally provided which is received within the socket of the replaceable point, the two being fastened together by means of a removable lock. Normally, 5 to 10 replaceable points are used during the life span of the adapter.
Starting about 25 years ago, efforts were made to extend even further the life of the adapter--it being appreciated that this is a relatively heavy element and that considerable down time of valuable equipment may be required for its replacement. One such effort is seen in Peklay U.S. Pat. No. 2,896,345 wherein the wear cap was provided on the top surface of the adapter and held in place by means of the cooperation of a tongue and groove connection along the sides of the wear cap and adapter and the projection of the top wall of the point. This proved inadequate because the constant flow of material over the wear cap wore away the metal, particularly along the sides of the top of the cap. This threatened the central dovetail connection and led to the improvement set forth in Hill U.S. Pat. No. 3,082,555.
An important distinction in the Hill U.S. Pat. No. 3,082,555 was the enthickening of the cap along the sides in an attempt to prolong the wear life of the cap. This also proved unsuccessful so the Hill construction was modified to eliminate the angled bottom sides of the cap and to extend the depending tongue the full length of the cap so as to provide for reversibility--the thought being that the live could be effectively extended by reversing the cap after the dovetail connection at the forward end had become threatened. This reversible modification of the Hill '555 construction has been widely utilized for the last 15 years or so.
Even though the reversible feature provided the advantage of a somewhat extended wear life, it maintained the disadvantage of the Hill construction over the Pecklay construction in continuing to expose the connection between the cap and adapter at the cap forward end. This meant that material flowing rearwardly over the tooth had the opportunity of entering into the space between the surfaces providing the dovetail connection and creating wear which could lead to looseness and premature failure.
Furthermore, in the oft-repeated event of inadequate maintenance--as where these wear caps were not replaced soon enough, the forward end of the wear cap dovetail become partially worn away. This proved catastrophic to the service life of the adapter because it would no longer retain wear caps.
This has been avoided by the instant invention which, in a sense, is a partial return to the Pecklay '345 construction by virtue of having a closed forward end on the wear cap so as to protect the bearing surfaces constituting the connection between the cap and adapter. However, two significant differences characterize the invention over Pecklay '345. First, the bearing surfaces of the cap/adapter connection are no longer dovetailed but are "horizontal", i.e., parallel to each other on the opposite sides of the cap and, more particularly, a massive section has been added at the very front of the cap which is characterized by forwardly extending side projections. These projections effectively extend the life of the cap by installing more wear metal at the point of crucial wear, i.e., just forward of the side rail connection. Thus, it will take correspondingly longer before flowing earth which can be quite abrasive, can enter into the spaces between the bearing surfaces of the connection. Additionally, the parallel bearing surfaces provide effective retention of wear caps even where their forward end has worn when a wear cap has been allowed to wear through. Here it should be appreciated that close fits between interconnected parts are impossible not only because of the production of these parts by casting but also because the interconnected parts may have different degrees of wear.
The provision of the forward projections on the cap generated an additional benefit in the fact that the generally cup-shaped forward contour generated by these projections provided a barrier which induced buildup of material on the top of the point in the crucial central rear area about the pin lock. This is the location of incipient failure because of the removal of material for the pin lock and also because of the repetitive stresses which are localized in this area.
Although the concept of providing a barrier at the rear of the point to develop a buildup is not new--see Stratton U.S. Pat. No. 2,987,838, it has not been utilized in commercially available excavating teeth. More particularly, when Stratton attempted to provide this function through the use of a wear cap, he provided no forward projections, no closed forward end and utilized the inferior dovetail connection between the cap and adapter.
It should also be appreciated that wear caps having parallel side rails or wings to enter into grooves on the side of the adapter have also been known for a substantial period--see Patersen U.S. Pat. No. 2,968,880. However, this construction has also failed to reach commercial significance not only because of the flimsiness of the sheet metal cap but, more importantly, the fact that the cap was not closed at the front so as to protect the important connection along the sides of the cap and adapter.